In cold climates, water in plumbing systems tends to freeze and expand when exposed to temperatures below freezing. When structures are vacant or when water pipes are either exposed or located in attics or exterior walls, the expansion of frozen water may cause the pipes to rupture, leading to water damage when the pipes thaw and water flow resumes.
Keeping water moving throughout the system is effective in preventing water from freezing in the pipes during a cold spell. Hence, people open faucets to drip, maintaining water movement. However, this practice wastes water and may cause water pressure problems.
Prior art methods use circulating water to prevent frozen pipes. U.S. Pat. No. 4,672,990 describes a system with restrictive connections between the hot water and cold water supply lines. However, migration of water between the lines would result in "warm" cold water and "cool" hot water. Further, the increased pressure caused by the circulating pump could pump water back into the main water supply, contaminating it.
U.S. Pat. No. 5,318,059 describes a method of warming cold water by mixing it with hot water and conducting it to the cold water main line. Again, the homeowner would get "warm" cold water or "cool" hot water.